The present disclosure relates to defect detection within manufactured goods, and more specifically, to determining the most effective order in which to address discovered defects.
Improving yield increases manufacturing efficiency, which reduces waste and cost, and improves reliability. Yield is the percentage of non-defective products produced by a process. Related to yield is the concept of failure, which is an electrical signature causing a device to malfunction (which can be obtained by electrical testing, for examples, power shorts, input/output (I/O) pin open, automatic test pattern generation (ATPG) failure or scan chain failure etc., for logic; and single cell failure (SCF), vertical pair failure (VPF) and horizontal pair failure (HPF) etc., for static random access memory (SRAM)). Further, a defect is a physical abnormality causing such an electrical signature. The methodologies of identifying a defect include failure analysis, which includes the electrical and physical processes preformed to identify the defect for the failure, or matching hits, which is the process of matching the inline inspection physical defect maps with functional test failure maps (bit fail map). Additionally, there can sometimes be No Defect Found (NDF) after failure analysis, or no inline inspection defect correlated to an electrical failure.
As advanced semiconductor technology becomes more complicated, the types of defects are increasing and the root cause identification and resolution for each type of defect also becomes more challenging. In order to achieve fast yield improvement under this situation with so many types of defects and limited resources, it is important to deploy the limited resources to focus on the defects with the greatest yield impact.
Yield can be defined using different concepts including functional considerations (whether the device has the intended functionality, e.g., performs the functions it is designed to perform), and parametric considerations (whether the device performs within the intended operating range, e.g., speed, power, voltage, resistance, temperature, etc.); and yield can also consider production efficiency. Defects that reduce yield can occur because of faulty designs and/or faulty manufacturing. Therefore, design yield can be found by looking to the functional and parametric components; while manufacturing yield looks to the percentage of items that are produced without physical defects, and is generally discovered by physically, visually, or electrically testing the manufactured product.
The concept of defect limited yield (DLY) is the ratio of product that meets functional specifications to the total product made, and is contrasted with the concept of circuit limited yield (CLY) which is the ratio of the product that meets or exceeds performance specifications to the total product made. The systems and methods discussed below relate to such yield considerations.